Agonists for PPARα are used clinically to reduce triglycerides and improve high-density lipoprotein (HDL) cholesterol levels in patients with hyperlipidemia. Whether the mechanism of PPARα activation to lower serum lipids occurs in the liver or other tissues is unknown. To determine the function of hepatic PPARα on lipid profiles in diet-induced obese mice, we placed hepatocyte-specific peroxisome proliferator-activated receptor-α (PPARα) knockout ( PparaHepKO) and wild-type ( Pparafl/fl) mice on high-fat diet (HFD) or normal fat diet (NFD) for 12 wk. There was no significant difference in weight gain, percent body fat mass, or percent body lean mass between the groups of mice in response to HFD or NFD. Interestingly, the PparaHepKO mice on HFD had worsened hepatic inflammation and a significant shift in the proinflammatory M1 macrophage population. These changes were associated with higher hepatic fat mass and decreased hepatic lean mass in the PparαHepKO on HFD but not in NFD as measured by Oil Red O and noninvasive EchoMRI analysis (31.1 ± 2.8 vs. 20.2 ± 1.5, 66.6 ± 2.5 vs. 76.4 ± 1.5%, P < 0.05). We did find that this was related to significantly reduced peroxisomal gene function and lower plasma β-hydroxybutyrate in the PparaHepKO on HFD, indicative of reduced metabolism of fats in the liver. Together, these provoked higher plasma triglyceride and apolipoprotein B100 levels in the PparaHepKO mice compared with Pparafl/fl on HFD. These data indicate that hepatic PPARα functions to control inflammation and liver triglyceride accumulation that prevent hyperlipidemia.

Biliverdin reductase (BVR) is an enzymatic and signaling protein that has multifaceted roles in physiological systems. Despite the wealth of knowledge about BVR, no data exist regarding its actions in adipocytes. Here, we generated an adipose-specific deletion of biliverdin reductase-A (BVRA) (BlvraFatKO) in mice to determine the function of BVRA in adipocytes and how it may impact adipose tissue expansion. The BlvraFatKO and littermate control (BlvraFlox) mice were placed on a high-fat diet (HFD) for 12 weeks. Body weights were measured weekly and body composition, fasting blood glucose and insulin levels were quantitated at the end of the 12 weeks. The data showed that the percent body fat and body weights did not differ between the groups; however, BlvraFatKO mice had significantly higher visceral fat as compared to the BlvraFlox. The loss of adipocyte BVRA decreased the mitochondrial number in white adipose tissue (WAT), and increased inflammation and adipocyte size, but this was not observed in brown adipose tissue (BAT). There were genes significantly reduced in WAT that induce the browning effect such as Ppara and Adrb3, indicating that BVRA improves mitochondria function and beige-type white adipocytes. The BlvraFatKO mice also had significantly higher fasting blood glucose levels and no changes in plasma insulin levels, which is indicative of decreased insulin signaling in WAT, as evidenced by reduced levels of phosphorylated AKT (pAKT) and Glut4 mRNA. These results demonstrate the essential role of BVRA in WAT in insulin signaling and adipocyte hypertrophy.

Heme oxygenase (HO) plays an important role in the cardiovascular system. It is involved in many physiological and pathophysiological processes in all organs of the cardiovascular system. From the regulation of blood pressure and blood flow to the adaptive response to end-organ injury, HO plays a critical role in the ability of the cardiovascular system to respond and adapt to changes in homeostasis. There have been great advances in our understanding of the role of HO in the regulation of blood pressure and target organ injury in the last decade. Results from these studies demonstrate that targeting of the HO system could provide novel therapeutic opportunities for the treatment of several cardiovascular and renal diseases. The goal of this review is to highlight the important role of HO in the regulation of cardiovascular and renal function and protection from disease and to highlight areas in which targeting of the HO system needs to be translated to help benefit patient populations.

Global obesity has nearly tripled over the last five decades, leading to comorbidities such as non‐alcoholic fatty liver disease (NAFLD), insulin‐resistant diabetes, and cardiovascular disease. Pharmaceutical interventions remain limited, and many anti‐obesity therapeutics such as sibutramine may be associated with deleterious cardiovascular outcomes. There is an urgent need for new, effective, and safe therapeutic strategies for obesity and comorbidities such as NAFLD. Our previous work has shown that bilirubin functions as a hormone by binding directly to the PPARalpha nuclear receptor to reduce adiposity and NAFLD, which suggests that it might have a potential therapeutic use. However, bilirubin is very hydrophobic, which lowers its translation potential. Bilirubin nanoparticles, a soluble form of bilirubin made by PEGylating bilirubin (PEG‐BR), can be dissolved in saline. We treated diet‐induced obese mice with NAFLD by IP injection with the bilirubin nanoparticles (30 mg/kg every 48 hours) or vehicle for four weeks. We found that bilirubin nanoparticle treatment improved hepatic function in obese mice with NAFLD by lowering AST and ALT, biomarkers of liver dysfunction. Lipidomic analysis of the livers using mass spectrometry showed remodeling of the hepatic lipid profile and significantly reduced (p<0.05) ceramide and dihydroceramide lipid species in obese mice treated with bilirubin nanoparticles. We found that bilirubin nanoparticles activated PPARalpha and ACOX1 to induce fatty acid β‐oxidation. Further analysis of the metabolome using a Bruker In Vitro Diagnostic Research platform with nuclear magnetic resonance spectroscopy showed significantly increased (p<0.05) plasma ketone β‐hydroxybutyrate concentrations in subjects treated with bilirubin nanoparticles. These data suggest that bilirubin nanoparticles activate the PPARalpha‐induced transcriptome to remodel the hepatic lipid profile, increase fatty acid β‐oxidation, and use of these metabolites for the generation of ketones. These data indicate that bilirubin nanoparticles may be used as a potential therapeutic for NAFLD.

Degenerin proteins, such as βENaC and ASIC2, and Transient Receptor Potential Channel 6 (TrpC6) have been implicated in cardiovascular function. However, their roles and potential interaction in metabolic disease has not been studied. To begin to assess this interaction, we evaluated the impact of a high fat diet (HFD) on in mice lacking normal levels of ASIC2, βENaC and TrpC6. Twenty week old male and female mice were placed on a 60% HFD for 12 weeks. Body weight was measured weekly, body composition by non‐invasive ECHO MRI and fasting blood glucose were measured at 0, 4, 8 and 12 weeks. A glucose tolerance test was administered after 12 weeks. Differences between ASIC2/βENaC/TrpC6 and WT groups were compared using independent t‐tests within each sex. Data are presented as mean ± SEM, ASIC2/βENaC/TrpC6 vs. WT. At 20 weeks of age, female ASIC2/βENaC/TrpC6 mice (n=6) weighed less (22.7±1.0 vs 26.3±0.8g, p=0.029) and gained less weight (12.1±1.7 vs. 20.5±1.3g, p=0.004) than WT (n=5). Total body fat (16.2±2.0 vs 23.2±1.1g, p=0.017) and lean body masses (19.2±1.0 vs 24.8±0.7, p=0.0014) were reduced in female ASIC2/βENaC/TrpC6 mice. In contrast, male ASIC2/βENaC/TrpC6 (n=5) mice had similar body weight (34.1±0.8 vs. 36.8±1.8g, p=0.165) at 20 weeks and 12 week HFD weight gain (11.8±1.5 vs. 12.1±0.9g, p=0.881) compared to WT (n=4). Fasting blood glucoses were lower in female (166±6.4 vs.212±5.3 mg/dL, p=0.0004) and male (181±2.8 vs.210±9 mg/dL, p=0.006) ASIC2/βENaC/TrpC6 mice after 12 weeks HFD. The area under the curve for the glucose tolerance test was reduced in female (18263 ± 510 vs 34623±4719 min.mg/dL), but increased in male (26100±1639 vs. 19408±1364 min.mg/dL) ASIC2/βENaC/TrpC6 mice. Liver (0.83±0.05 vs. 1.93±0.34g, p=0.0066) and liver fat (0.011±0.007 vs.0.333±.158, p=0.05) masses, as well as percent liver fat (1.1±0.6 vs. 14.4±4.1%, p=0.006), were reduced in female ASIC2/βENaC/TrpC6 mice after HFD. While liver (1.77±0.13 vs. 2.49±0.15g, p=0.007) and liver fat (0.17±.06 vs. 0.37±.03g, p=0.044) masses were reduced in male ASIC2/βENaC/TrpC6 mice, percent liver fat was not statistically lower (8.8±2.6 vs. 14.7±0.7%, p=0.11). These highly novel findings suggest that ASIC2, βENaC and/or their interaction with TrpC6, protects against HFD induced‐metabolic disease in female, but not male, mice. The mechanisms underlying this response will be examined in future studies.Support or Funding InformationThis work was support by NIH P01HL051971, P20GM104357, P20GM121334 and R01HL136684.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Several population studies have found lower serum bilirubin levels to be associated with the pathology of metabolic-associated fatty liver disease (MAFLD). Yet, treatments to target this metabolic trend have not been explored. In our study, we hypothesized that inhibition of hepatic UGT1A1 would increase serum bilirubin levels and improve conditions like MAFLD and hepatic insulin resistance. Therefore, we designed an RNAi targeting murine Ugt1a1 expression in the liver. The RNAi molecule was constructed by conjugating it with an amino sugar derivative of galactose, N-Acetylgalactosamine (GalNAc) [GalNAc-UGT1A1-RNAi]. GalNAc covalently linked to the siRNA enables delivery through the asialoglycoprotein receptor (ASGPR)-mediated targeting to hepatocytes in vivo. Hence, the treatment of the GalNAc-UGT1A1-RNAi primarily targets the liver. In this study, male C57BL/6J mice were fed a high-fat diet (HFD, 60%) for 30 weeks for diet-induced obesity (DIO) and were treated subcutaneously with GalNAc-UGT1A1-RNAi (3mg/kg, n=7) or sham control (n=6) once weekly the final 4 weeks while on the HFD. The results show that GalNAc-UGT1A1-RNAi treatment significantly raised serum bilirubin levels compared to sham control-treated (0.38±0.01 vs. 1.36±0.08 mg/dL, Sham vs. GalNAc-UGT1A1-RNAi, p<0.05), decreased hepatic fat content (26 ± 1.4 vs. 18 ± 1 %, p<0.05) and hepatic triglycerides (17±1.5 vs. 11.5±1 nM, p<0.05), and improved fasting blood glucose (261±11 vs. 201±8 mg/dL, p<0.05) and insulin (9.9±0.1 vs. 3.5±0.3 ng/ml, p<0.05) levels. We performed extensive kinase activity analyses using PamGene PamStation technology and found a significant increase in insulin receptor downstream mediators such as SRC, AKT, and ERK kinase families with the GalNAc-UGT1A1-RNAi treatment, indicating improved hepatic insulin sensitivity. These results show that GalNAc-UGT1A1-RNAi improves MAFLD, increases serum bilirubin, reduces its catabolized produce urobilin in the plasma, and reduces hyperglycemia and hyperinsulinemia. These indicate that UGT1A1 antagonism might serve as a treatment for MAFLD and hepatic insulin resistance, which could improve obesity-associated comorbidities. This work was supported by the National Institutes of Health 1R01DK121797-01A1 (T.D.H.) and 1R01DK126884-01 (D.E.S.), the National Heart, Lung and Blood Institute K01HL-125445 (T.D.H.) and P01 HL05197-11 (D.E.S.), and the National Institute of General Medical Sciences P20GM104357-02 (D.E.S.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.